1. Field of the Invention
The present invention relates to a novel motor using superconductive materials, in particular to a motor apparatus provided with cooling means.
2. Description of the Prior Art
In the conventional squirrel cage induction motor a short-circuit looped in itself is formed in a squirrel cage rotor comprising a plurality of bar conductor short-circuited by two circular conductors opposite to each other at both ends thereof and power-supplied by an electro-magnetic induction from a stator side to generate a torque. Accordingly, the squirrel cage rotor is rotated at a speed of rotation slightly smaller than that of a rotational magnetic field generated by the stator.
On the other hand, in a synchronous motor a rotational magnetic field is generated by a stator similar to that in an induction motor. At starting, a rotor is rotated in the principle similar to that in the induction motor to start the synchronous motor and then the rotor (field) is excited by a direct current to rotate the rotor at the same speed of rotation as that of a rotational magnetic field generated by the stator, that is, synchronously.
FIG. 1 is a sectional view taken along the plane including an axis of rotation, showing a construction of the above described conventional general squirrel cage rotor;
FIG. 2 is a partial developed view taken along the rotational direction by the line II--II in FIG. 1; and
FIG. 3 is a partial sectional view taken along the direction meeting with the axis of rotation at right angles, showing a construction of an iron core.
An iron core 1 is formed of a large number of electromagnetic sheet steels stuck together or cast cylindrically.
The iron core 1 is firmly mounted on a motor shaft 6 by two clampers 3 from both sides thereof in an axial direction thereof so that a center axis thereof may coincide with a center aixs of the motor shaft 6.
A plurality of slots 2 are formed in a direction along the center axis of the iron core 1 by punching or machining so as to pass through the iron core 1, as shown in FIG. 2 showing a sectional view taken along the direction meeting with the center axis at right angles.
Bars 4 made of metallic conductors formed of, for example, copper, aluminum or alloys thereof and the like are inserted into the respective slots 2. And, end rings (circular conductors) 5 made of the metallic conductors similar to the bars 4 are connected to both ends of the respective bars 4 by brazing or welding to electrically short-circuit, whereby constructing the squirrel cage rotor (secondary circuit) of the induction motor.
In the induction motor using the conventional squirrel cage rotor having such the construction, the squirrel cage rotor has a resistance, so that, as shown in FIG. 4(1) showing torque-speed characteristics, if a voltage is applied, the induction motor is started wth overcoming a load and gradually accelerated until the speed close to the synchronous speed, and then rotated under the well-balanced condition with the load torque with keeping the slip so that the speed of rotation may be slightly smaller than the synchronous speed by designing various kinds of factor so that a starting torque larger than the load torque (4) may be generated.
Now, in the general motor, in order to improve the starting characteristics, the secondary resistance is increased but if the size of the conductor is increased, the heat capacity is increased. On the contrary, in the induction motor using the squirrel cage rotor in the above described manner the resistance of the squirrel cage rotor as the secondary resistance has not been made variable. Accordingly, a problem occurs in that if the squirrel cage rotor is large-sized with fixing the resistance thereof, an electric loss, which is proportional to the large secondary resistance, is generated also in the constant-speed driving after the completion of starting, so that the driving efficiency is remarkably reduced.
On the other hand, the synchronous motor is advantageous from viewpoints of the efficiency and the power factor during the driving after the starting thereof but problems occur in that the insulation of the field coil is required, the construction being complicated on account of such the requirement, and the provision of also damper windings being required for the starting stability and the transition stability as the induction motor, whereby the conductor cannot take such the large size as the squirrel cage rotor in the usual induction motor, also the starting torque being limited, and the like.